The present invention relates to an apparatus for automatically measuring the resistance and heating up of resistive electrical components.
It relates more particularly to measuring the resistance and heating up of the windings of transformers or the coils of motors. It also enables an indication to be given of the ambient temperature at the place where these various measurements are made.
Apparatus is known which enables measurements to be made, on the one hand, of the resistance of a resistive electrical component (e.g. a winding) and, on the other hand, of the heating up to which this winding is subject when it is for example subjected to operating tests. Apparatus which enables the resistance and heating up of a component to be measured is generally formed by a Wheatstone bridge whose arms contain variable resistors which have to be adjusted each time a measurement is made, so as to balance the bridge. Once the bridge is balanced, it is then necessary, from the value to which one of the resistors has been adjusted either to calculate the temperature of the component contained in one of the arms of the bridge, or to calculate the value of the resistance of this component, after the bridge has been rebalanced. These adjustments are time consuming and require care and they result in a considerable disadvantage. Because the time required to perform the balancing operation is fairly long, a component whose temperature is to be measured after an operating test cools down to a considerable extent and the amount of heating up calculated on the basis of balancing the bridge is less than the actual heating up which the component has experienced at the end of the test.
Furthermore, if the ambient temperature at the place where the tests are being conducted varies, it is necessary to be able to detect these variations very quickly, indeed virtually at the same time as the measurements of the heating up of the components are carried out. There is no known apparatus which enables highly accurate measurements to be made of variations in ambient temperature, virtually at the same time as measurements of the heating up of the components and using the same apparatus.
One object of the invention is to provide an apparatus for automatically measuring the heating up and resistance of resistive electrical components which enables these drawbacks to be substantially reduced or overcome, and in particular enables difficult and time consuming adjustments to be avoided the effect of which is that the heating up measured is less than the actual heating up of the component at the end of the test.
Another object of the invention is to enable virtually simultaneous measurements to be made of the heating up of the component and of the ambient temperature at the place where the tests and measurements are being performed. Finally, the invention avoids the necessity of rebalancing the bridge, each time the heating up of a component is to be measured.